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Multi-drop SMBus Config.

Ed P.
Prodigy 90 points
Other Parts Discussed in Thread: BQ2083, PCA9544A

I am designing a four battery back up system using Li+ batteries containing two separate 4p3s strings, each monitored by bq2083/bg29311 chip sets. The default slave address for every string is the same. Is there a way to identify and communicate with each 2083 using a multi-drop SMBus architecture?  

  • 0
    TI__Prodigy 480 points

    You need an I2C or SMBus multiplexer/selector.  This should do what you need. 

    http://focus.ti.com/lit/ds/symlink/pca9544a.pdf

     

     

  • 0 in reply to TravisN
    Prodigy 90 points
    A document provided by the battery manufacturer (UltraLife) suggests that the first SMBus battery to be recognized on the bus will keep the default SMBus battery address and the rest can dynamically be assigned addresses as they are recognized. I am unable to verify this in the System Management Bus Spec. or the Smart Battery Data Spec. To your knowledge, is this true? Can I overwrite the Device ID/Slave address of the BQ2083?
  • 0 in reply to Ed P.
    TI__Prodigy 480 points

    No you cannot change the device address of the bq2083.  For a battery to conform to smbus specification it must be address 0x16/0x17 (8 bit)  or as in the 7 bit smbus device address 0001011binary  with the LSBit a 0 for a write and a 1 for a read.  If you were able to change the device address then you would not be conforming to smbus so the address is fixed to 0x16 in all our fuel gauges.  Im not sure what ultralife is talking about but perhaps they are talking from behind a multiplexer or selector of some kind

  • 0 in reply to TravisN
    Prodigy 90 points
    Thanks, that was my understanding of the specification.